Amelioration of magnesium deficiency in a Norway spruce stand (Picea abies) with calcined magnesite

Norway spruce has shown needle yellowing and defoliation symptoms on many sites of the Bohemian Forest in north central Austria since the early 1980s. A forest amelioration experiment was set up to evaluate the response of spruce to magnesite based fertilizers with different solubilities. Response variables were a crown vigor index, diameter growth, nutrient contents in needles, soil solution chemistry, and soil chemistry. Soil solution at fertilized plots showed an immediate response in base cation concentrations, nitrate concentrations and pH-values. Fertilization increased the pool of exchangeable cations in the upper 15 cm of the soil and reduced levels of exchangeable Al. The magnesium and calcium content of the needles of dominant trees was greatly improved. Fertilization has increased the mineralization rate of soil organic matter. Diameter growth, as a measure of tree vigor, showed a pronounced positive response with a time delay of 5 years. Our results demonstrate that magnesite based fertilizers are a viable option to improve the nutritional status of spruce forests on granitic bedrock.